As the others have said:

- Meet at a somewhat public place like a parking lot at a store, gas station, ???
- If you are meeting someone from a site like this one that has a feedback section, check there first - as it was also stated, this is a pretty tightly knit group that will rat out a bad egg pretty quickly.
- It's never a bad idea to have someone with you to help keep an eye out for anything that doesn't look quite right about the situation.
- There's nothing requiring a bill of sale by law, but if you decide that you will require one for your records, make sure you make it very clear before a meeting is set up as with some people it will be a deal breaker. If I'm dealing with someone that I haven't met previously, I will ask to see their ID to verify residency, and in some cases to make sure they are of legal age to purchase.

Word of mouth sales to people you know are always a good idea as well. Good luck!